bonrud



March 31, 1964 0, BONRUD 3,127,333

REPRODUCTION SYSTEM Filed May 29, 1961 //Vl/N70/Q [EON Q 150N200 United States Patent 3,127,333 REPRODUCTION SYSTEM Leon 0. Bonrud, Minneapoiis, Minn, assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware Filed May 29, 1961, Ser. No. 113,290 16 (Zlaims. (Cl. 204-18) The present invention relates to a new and useful reproduction system. In one aspect the invention relates to a new reproduction receptor surface, such as a copysheet. In another aspect this invention relates to a new process for the reproduction of an image pattern.

One of the most recently developed methods for the reproduction of images utilizes a receptor surface containing a photoconductor which is exposed to the pattern to be reproduced and is thereafter electrolytically developed. One of the usual forms of the reproduction surface is a copy-sheet upon which has been deposited a metal layer and upon which metal layer has been bonded with an insulating resin a photoconductor, such as zinc oxide. This sheet is then exposed to a light pattern or a light image and then electrolytically developed. The electrolytic development is accomplished by connecting the negative pole of a direct current source to the metal layer of the sheet. A liquid solution containing an elec trolyte and a developer material is contacted with the exposed surface of the copy-sheet and the positive pole of the direct current source is connected to the electrolytic solution. Electrolysis is effected in the solution resulting in a deposit of the image on the surface of the copysheet. The theory behind the process involves the change in conductivity of the photoconductor upon exposure to light. The pattern formed by the light-struck areas is more conductive than the non-light-struck areas. Therefore, when electrolytic solution contacts the surface during development, the current passes during electrolysis through the light-struck areas of the photoconductor. The developer solution may contain a metal salt which is reduced and the metal is deposited upon the lightstruck areas due to the current.

One of the controlling factors in the successful operation of the electrolytic process is the resistance of the receptor laminate containing the photoconductor to the passage of current during electrolysis. In order to produce a receptor having a sufficiently low resistance for the electrolytic development of the reproduction, special photoconductors of high photoconductivity are used. These photoconductors are characterized by the fact that the surface coating of the receptor has a conductivity of at least l0- mho/cm. in the light. Photoconductors which provide a receptor of such conductivity are usually satisfactory for the electrolytic process. The correlation of the conductivity of the photoconductor and the thickness of the photoconductive coating is necessary to provide a minimum of resistance to the passage of electrical current during electrolysis.

Even with such precautions as described above, the electrolytic process has certain limitations as a result of the surface resistance between the photoconductive coating and the electrolytic solution. This surface resistance observed between the photoconductive coating and the electrolytic solution increases the overall resistance of the laminate; and, therefore, places a serious limitation on the use of the electrolytic process. It is much to be desired, therefore, to provide a receptor construction which will reduce this surface resistance.

In addition, the photoconductors which are usable as the surface coating on the receptor for an electrolytic .process are preferably of the N-type and, therefore,

characteristically rectify the current during electrolytic development. Thus, the receptor must be the negative pole 3,127,333 Patented Mar. 31, I964 and the electrolytic solution the positive pole. This type of a cathodic reproduction of the image is characteristic of the electrolytic process with certain photoconductors. Connecting the receptor with the positive pole and the electrolytic solution with the negative pole usually results in an unsatisfactory process because rectification causes increased resistance to the flow of the electrical current. Although current may flow under anodic development, generally the time required is excessively long, and the difierentiation between the light-struck areas and nonlight-struck areas is such as to cause a poor image reproduction. It is, therefore, much to be desired to provide a receptor construction which will minimize or elimihate this rectification effect and thus permit anodic development as well as cathodic development of the image on the receptor.

The object of this invention is to provide a new electrolytic-type receptor material.

Another object of this invention is to provide an electrolytic receptor material or copy-sheet which has decreased resistance to the passage of current during elec' trolytic development of the image on the receptor.

Still another object is to provide a new and improved photoconductive receptor of increased conductance or sensitivity.

Yet another object is to provide a photoconductive receptor of improved light memory.

Another object is to provide a black photoconductive receptor useful for making positive reproductions.

Another object of this invention is to provide a process for the electrolytic development of a latent reproduction.

Still another object of this invention is to provide an anodic process for the electrolytic development of a latent reproduction.

Various other objects and advantages of the present inventiton will become apparent to those skilled in the art from the accompanying description and disclosure.

In accordance with this invention, a photoconductive receptor is utilized to reproduce an image or pattern by exposing the receptor to a radiation pattern or light image and by electrolytically developing the resulting latent image or pattern on the receptor sheet, either cathodically or anodically. The receptor sheet comprises a photoconductive layer bonded to a continuous smooth metal layer or substrate. The metal substrate may be affixed to a non-conductive backing, such as paper or plastic, but this is not always necessary in every case. Upon the photoconductive layer, and substantially coextensive therewith, is bonded a radiation penetrable conductive layer which usually comprises an admixture of conductor particles and binder. The conductive layer has greater conductivity in at least one direction than does the photoconductive layer under irradiation, and the conductive layer is in itself usually not substantially photoconductive or light-responsive. The result is that the interface between the receptor and the electrolytic solution oiiers less resistance to the passage of current during electrolytic development than would be the case were such top conductive layer not present. In addition, the receptor has increased light memory.

The conductive top or outer layer of the receptor laminate preferably has a conductivity (measured in its forward direction or in direction of least resistance to current, if it has such a characteristic) of more than 10* mho/cm. in the light or under irradiation and preferably greater than the conductivity of the photoconductive layer. The conductive layer usually has a conductivity (in its backward direction, if it has such a characteristic) of at least 10- mho/cm. or greater, while the photoconductive layer has a cathodic conductivity (forward direction) usually between lO and 10' mho/cm., under irradiation conditions. Typical materials which 3 provide the above properties in the top conductive layer include semi-conductors and conductors such as carbon black; conductive zinc oxide; cadmium oxide, titanium oxide, titannous oxide, lead sulfide and manganese dioxide; metal powders when admixed with an insulating resin or electrolytically deposited in granular form, such as clean aluminum, tin, copper, silver and chromium powders. The semi-conductors of the above group which have been utilized in the invention appeared to be of the N-type. Conductive zinc oxide may be prepared by the method described in Patent No. 2,887,632 issued May 19, 1959, and by other conventional methods. With conductors and certain semi-conductors, the conductance of the receptor measured in the backward direction relative to the photoconductive layer is greater than when no conductive top layer is present and the photoconductive layer is the top layer. Therefore, in some instances such as with a top layer containing metals, carbon black, conductive zinc oxide or cadmium oxide, the effective conductivity in the backward direction of the receptor will also be more than mho/cm. In this connection, photoconductive layers such as zinc oxide, generally have an effective anodic conductivity less than lO mho/ cm.

Conductivity (or resistivity) is determined by connecting the receptor to the negative pole for determining cathodic conductivity or to the positive pole for determining anodic conductivity and measuring the current for a given voltage with an aqueous electrolytic solution as the other pole or electrode. The thickness of the layer or layers being measured is used to extrapolate to a standard thickness of one centimeter. The conductivity showing the lowest value would be that characteristic of the flow of current in the backward direction (rectification, if any).

The conductive top layer is deposited on the photoconductive layer by means of a resinous binder incorporated with the conductive particles in such thickness that at least 10 percent of the radiation utilized for producing the differentially-conductive pattern on the photoconductive layer penetrates the top layer to the photoconductive layer. Preferably, at least percent penetrations is desired. The thickness and composition (kind and quantity of a conductive material and binder) of the conductive layer is such that the transverse resistance, in the forward direction, of the combined photoconductive layer and conductive top layer is less than 25,000 ohm cm. Generally, the top conductive layer, itself, will have less than 200 ohm crn. preferably between about and about 1 ohm cm. resistance in the forward direction. In comparison, the transverse resistance of the photoconductive layer itself, in the forward direction (measured without the presence of a top conductive layer and in an electrolytic solution), is usually above 500 ohm cm. such as 1000 ohm cm. or higher. The overall transverse resistance (in forward direction) of the receptor containing a top conductive layer will usually be less than that of the photoconductive layer due to the decrease in surface resistance between the top layer and the electrolytic solution.

When the receptor is to be used in a system in which the current is passed in the backward direction to the photoconductive layer, the thickness and composition of the conductive layer must also be such that the transverse resistance measured in the backward direction of the combined photoconductive layer and the combined layer must be less than 25,000 ohm cm. In such case, a conductive material is used in the top layer that has a backward conductivity of at least 10 mho/cm. The rectification of the receptor is then determined by the top conductive layer and not the photoconductive layer which is no longer in contact with the electrolytic solution.

In case a receptor is to be used for a positive reproduction, a black or dark conductive material is used. Carbon black is suitable for this purpose, and also carbon black reduces both the forward and backward resistances of the receptor. Electrolytically-deposited silver as the top layer is black, and is similarly useful. In the case of silver, a deposit of silica from a colloidal suspension of same on the photoconductive layer, followed by electrolytically depositing silver, increases the blackness of the top layer.

In addition, the composition of the top conductive layer is such that the lateral or surface resistance of the receptor is greater than 10,000 ohm per square; preferably at least 100,000 ohm per square, but generally is not higher than about 500,000 ohm per square. It is essential that the lateral resistance of the top layer be relatively high in order to prevent blurring of the image. In general, the thickness of the conductive layer is between about 0.1 and about 10 microns.

The photoconductive layer which is deposited on and bonded to the metal layer utilizes a suitable photoconductor which will result in a differentially conductive pattern corresponding to the original pattern upon exposure to irradiation. The photoconductors are such that the photoconductive layer has a conductivity of at least 10* mho/ cm. on exposure to radiation. The thickness of the photoconductive layer is usually between about 0.5 and about 2 mils. The photoconductors are applied to the metal layer in the form of powders or particles with a suitable insulating resinous binder. Photoconductors which can be utilized in particulate form and have sufficient conductivity for the electrolytic process include zinc oxide, indium oxide, mercuric oxide, cadmium sulfide and lead sulfide. The preferred photoconductors include the metal oxides, such as zinc oxide and indium oxide.

The metal layer may be sufficient as a self-supporting layer for the other layers of the receptor or may be bonded or afiixed to a backing for support or insulation purposes. Foils or films of metal are suitable as a selfsupporting metal layer. When a backing is utilized, the metal is deposited upon the backing or adhered thereto in the form of a film or foil. The metal layer may be deposited on the backing by vapor deposition, electroplating, precipitation, or by bonding metal particles thereto with a suitable binder. Conductance of the metal layer is important since the metal layer is used as one of the electrodes of the electrolytic process. Therefore, the metal layer must offer no more lateral or surface resistance than 1000 ohms, preferably no more than 10 ohms per square. The thickness of the metal layer, of course, will depend upon whether it is the support itself, or whether it is utilized merely as the electrode. When the metal layer is utilized upon a non-conductive backing, the thickness of the metal layer is usually be tween about 0.2 and about 1.5 mils when metal foil, and between about 0.01 and about 0.2 micron when vapor deposited. Suitable backing material for this metal layer is wood pulp paper, rag-content paper, and plastic films such as cellulose acetate films, Mylar films, polyethylene films and polypropylene films. Even cotton or wool cloth may be utilized as the backing without departing from the scope of this invention. Suitable metals for the metal layer include aluminum, tin, chromium, copper, silver and gold; preferably aluminum.

As previously discussed, insulating resinous binders are utilized to bond the particles together, as well as the photoconductive layer and the semi-conductive layer to the laminate receptor. The preferred resinous bonding agents are those which are no more conductive than either the photoconductor or the semi-conductor under dark conditions (in the absence of radiation). The resinous binder should also preferably have a low degree of wetability toward the photoconductive and semi-conductive particles. Suitable binders include the copolymer of styrene and butadiene (in a mol ratio of 70:30) known as Pliolite, polystyrene, chlorinated rubber (Parlon), rubber hydrochloride, polyvinylchloride, nitrocellulose and polyvinylbutyral. The binders used for the semiconductive layer may be more conductive than the semiconductor itself, thus contributing to the conductive characteristics of the semi-conductive layer. Therefore, the proportion and kind of binders for the semi-conductive layer are so chosen to give the desired conductive properties to the semi-conductive layer. In addition, to the above binders, other binders which can be used in the semi-conductive layer include Zytel-61 (Nylon) and silicone resin. The weight ratios of binder to photoconductive particles generally range from 1:10 to 1:1, preferably 1:5 to 1:2, and the weight ratio of binder to semiconductor particles generally ranges from :1 to 1:10, preferably 5:1 to 1:5, and depends upon the semi-conductor particles.

Sensitizing dyes may be incorporated with the photoconductive layer to enhance the response of the receptor to actinic light. Suitable dyes for this purpose include the phthalein dyes of xanthene class, such as Eosin (CI. 45380), Erythrosin (C.I. 45430), and Uranine (CI. 45350); thiazole dyes such as Seto Flavine-T (CI. 49005); sulfur dyes such as Calcogene Yellow 2. GCF (CI. 53160); quinoline dyes such as Calcocid Yellow 5 GL (CI. 29000); and heterocyclic dyes such as Phosphine-R (CI. 46005). The dyes may be used singly or in combinations of two or more dyes. A particularly good combination is Eosin and SetoFlavine-T. An amount of dye or dyes between about 0.001 and about 0.2 weight percent based on the photoconductor is satisfactory. The dyes are applied singly or in combination to the photoconductor from solutions such as from a solu tion of ethyl acetate.

In preparing the respective photoconductive and semiconductive layers, mixtures of two or more photoconductors or two or more semi-conductors may be utilized without departing from the scope of this invention. Similarly, two or more binders may be used in admixture.

As a means of illustrating the construction of the preferred receptor, the drawing which is provided shows a cross-section elevational view of such a construction. Element 11 is the non-conductive or insulating backing comprising paper or plastic film. A continuous and smooth metal layer of aluminum or the like afiixed to the backing 11 is illustrated by 12. The photoconductive layer comprising an admixture of binder and zinc oxide particles is indicated by 13, and the top or outer layer compirsing an admixture of a binder and the semi-conductor particles, such as carbon black or conductive zinc oxide, is indicated by numeral 14.

All of the layers 11 through 14 are securely bonded together to form a unitary receptor. The overall transverse resistance of the combined layers 14, 13 and 12, when conducting a current therethrough by means of an aqueous liquid electrolyte, should not be more than 25,000 ohms cm.

A typical construction of a suitable receptor is carried out as follows:

A 1mil thick aluminum foil 12 is adhered to a wood pulp paper backing 11 with a conventional adhesive. The paper is equivalent to twenty-pound weight. Photoconductive zinc oxide is admixed with Pliolite in a 30-percent solution of toluene. The suspension of zinc oxide in the binder solution is spread coated over the aluminum foil 12 which has been suitably cleaned to remove all dirt, grease and aluminum oxide by treatment with a dilute aqueous potassium hydroxide solution. The coating is allowed to dry and after drying, the thickness is about 0.8 mil. On this photoconductive coating 13 is applied another coating of a semi-conductor 14, such as carbon black or highly conductive zinc oxide. This semi-conductive coating is made up in a similar manner as a photoconductive coating and applied to the surface and permitted to dry. The thickness of the semi-conductive coating 14 is approximately 0.4 mil.

The photoconductive receptor of this invention is suitable for reproduction of an image by exposure of the receptor to a radiation pattern or light image. The radiation may be actinic light, ultraviolet light, Xrays and gama rays. As a result of exposure to the radiation pattern or light, a differentially-conductive pattern is formed on the receptor surface by virtue of the increased conductivity of the photoconductor in the light-struck areas. The difference in conductivity of the irradiated areas as compared to the non-irradiated areas is at least 10 times, and generally as much as times, or greater. Thereafter, the surface of the exposed receptor is contacted with a solution containing an electrolyte. A voltage is impressed across the electrolytic solution and the receptor while the receptor is in contact with a developer material which results in the reproduction of the image or pattern. In many instances, the developer itself constitutes the electrolyte, and no added electrolyte is necessary. In other instances, the liquid or solution, by virtue of its source, will contain an electrolyte. In case it is necessary to add an electrolyte to the solution, suitable electrolytes, such as sodium chloride, sodium carbonate, sulfuric acid, acetic acid or sodium hydroxide, may be used. The development may be carried out either anodically or cathodically. In other words, the receptor may be connected to the positive or negative source of direct current without departing from the scope of this invention. Metal plating by electrolysis is a typical example of cathodic electrolytic development of an image. In such instances, a suitable metal salt is dissolved in water and the surface of the receptor contacted with the aqueous solution, such as by inserting the receptor in a vessel containing the aqueous solution, or by brushing the solution on the surface with a sponge or gelatin roller or the like which is connected to a direct current source. Suitable metal salts which act both as an electrolyte and the source of the metal for plating purposes include copper sulfate, silver nitrate, silver chloride, nickelous chloride, zinc chloride, etc.

Other developer materials may similarly be utilized in the cathodic development of the image. For example, diazonium salts plus coupler materials in acidified water and diazotizable amines and coupler materials in water may be used. Also, the surface of the receptor may be treated with a suitable reducible dye, such as methylene blue, which is reduced during electrolysis.

As an example of anodic development, the receptor is made the negative pole, and the exposed surface is contacted with an aqueous latex containing negatively charged polymer particles, such as polyethylene and polypropylene, or a hydrosol of such materials as Anilin Blue and Indigo. The aqueous latex or hydrosol is connected to the opposite or positive pole. Those polymer latices which are stable in alkaline media usually contain negatively charged particles and are, therefore, operable in the anodic type of operation of the present invention. In this type of operation, the negatively charged particles are deposited selectively on the latent image pattern during electrolysis. Reproduction may be made on a white surface when the polymers of the latex contain a dye or coloring matter, such as a pigment. On black receptor surfaces, the polymer of the latex is usually white, and a positive is thereby produced directly. These reproductions employing a latex for the development are also useful as lithographic plates, since the light-struck areas containing the polymer thereon are hydrophobic.

Among other developers which may be used in the anodic process are substances capable of changing color on oxidation, such as the leuco form of vat dyestuffs used in the dyeing of various commercial fibers. For example, if the anodic process is carried out with Indigo white in contact with the exposed surfaces of the receptor, the anodic reaction oxidizes Indigo white from its colorless leuco form to insoluble colored Indigo in the conductive surface areas. The final visible image is found to be stable except for the tendency to fade slowly, probably because of the oxidation of the leuco dye on exposure to air. These dyestuffs can be incorporated into the elec trolytic solution or may be coated on the receptor surface prior to electrolysis.

, Still another developer material that may be employed in the anodic development process is the colored anion, as exemplified by the acid-type dyestuffs. By carrying out the electrolysis with the photosensitive sheet as the anode and with an acid-type dyestuff in the electrolytic solution, the colored anions of the acid-type dye migrate selectively to the conductive image areas and are deposited thereon, thereby coloring the light-exposed surface areas. These dyes are commonly marketed in the form of a salt of their sulphonic acid, usually the sodium salt. Illustrative of such developers are the mono-azo dyestuffs such as Fast Red (CI. 16575), the di-azo dyestuffs, such as Crocein Scarlet (C.I. 27290), the nitroso dyestuffs such as Naphthol Green (CI. 10025), the triphenylmethane dyestuffs such as Wool Green (CI. 44090), the xanthene dyestuffs such as Erio Fast Fuchsine BL (CI. 45190), the orthraquinone dyestuffs such as Solway Blue 26 (CI. 62125), the azine dyestuffs such as Azocarmine GE (CI. 50085) and the quinoline dyestuffs such as Quinoline Yellow (CI. 47005). Although some color is often deposited in the background areas when the colored anion containing electrolyte is brought into contact with the exposed photosensitive sheet surface, the depth of color is significantly greater in the light-struck areas and the contrast can be controlled by selection of the colored anion, concentration of colored anion in the electrolytic solution, duration and conditions of the electrolysis, etc.

The current necessary for development of the image by electrolysis is usually between about 1 and about 100 milliamperes per square centimeter. In general, the voltage required to give such a current through the electrolytic solution and receptor is between about 3 and about 100 volts, usually between to 60 volts per mil thickness of coating. The time required to'produce the visible reproduction by electrolysis is between about 0.1 second and about 1 minute, depending upon the current and the developer material utilized.

The specially constructed sheet material or receptor of this invention may also be utilized as a relay element or control in contact with a solid electrode of a photoelectric cell.

The following examples illustrate the method and construction of the receptor and the use of the receptor in the reproduction of an image or pattern in accordance with the present invention. The examples are not to be construed as unnecessarily limiting to the invention.

Example I A light-sensitive sheet material was prepared as follows: A flexible film of transparent Mylar having a thickness of about 2 mils was first metallized on one surface by vapor deposition in a vacuum, with an extremely thin coating of aluminum (about 0.05 micron). The coating was opaque and was found to have a surface resistivity of about 1 ohm per square. Over this metal layer was then applied a suspension of 38.4 grams of New Jersey Zinc Companys USP. 12 grade zinc oxide powder in a solution of 20 grams of toluene, 32 grams of ethyl acetate, 6.4 grams of Pliolite resin (a resinous copolymer of butadiene and styrene, serving as a binder) and 3.2 grams of polystyrene (also as a hinder), the mixture having been ball-milled with glass balls until smooth. The zinc oxide mixture applied to the aluminum surface also contained 1.9 ccs. of Eosin (1% in methanol) and 4.8 cos. of Seto Flavin-T (0.9% in methanol). The wet mixture was coated on the aluminum layer to a 4-rnil thickness in subdued light and then dried in the dark. The dry thickness of the zinc oxide coating was about 0.6 mil. The completed sheet material was highly water-resistant.

8 This receptor sheet had approximately the following electrical characteristics:

A. Measured with conductive rubber electrode (carbon black-in silicon rubberresistance, 20 ohm cm.) volts/miL- 10 (1) Effective average conductivity:

Dark mho/cm l0 Exposed (5 sec., 500 ft. candles,

3150 K.) mho/cm l0" (2) Estimated lateral surface resistance without conductive backing p/t Dark ohms per square 10 Exposed do 10 (3) Memory (dry):

Normalized conductance at 1 minute conductance at 1 minute conductance when light turned off B. Measured with electrolytic electrode Electrolyte Grams CUSO4'5H2O H SO 36N 15 H O distilled 540 (1) Effective average cathodic conductivity:

Dark 2.4 X 10* Inho/cm. at 31 v./mil.

Exposed 5 sec., 500 ft. candles, 3150 K. 1.2 X 10* mho/cm. at 6 v./ml. (2) Effective average anodic conductivity:

Dark 3.8 X 10 mho/cm. at 46 v./mil. Exposed 5 sec., 500 ft. candles, 3150 K. 4.2 X 10- mho/cm. at 46 v./mil. (3) Cathodic transverse resistance, pt:

=resistivity, ohm cm. t=thickness, cm.

Dark 6.9 X 10 ohm cm. at 31 v./mil. Exposed ohm cm. at 6 v./mil.

(4) Anodic transverse resistance, t:

Dark 4.4 X 10 ohm cm. at 46 v.mil.

Exposed 4.0 x 10 ohm cm. at 46 v./mil.

The sheet material prepared as described above was placed in a camera having a lens opening of f 4.5. The light on the subject was equivalent to 500 foot candles. The lens was focused on the subject at a distance of six feet. An exposure time of one second was used. The exposed sheet was then removed from the camera in the dark and placed in an aqueous electrolytic develop ing solution containing silver nitrate and thiourea. A 50-volt direct current potential was applied between the sheet and the electrolytic solution. The sheet was the cathode and the electrolytic solution was connected to a stainless steel anode. The development was carried out for one second at an average current density of about 15 milliamperes per square centimeter. A negative image was produced.

Example II The receptor sheet of Example I was modified by placing thereon a layer of carbon black as the top or outer layer to reduce the resistance during electrolysis and also provide a positive image.

After a zinc oxide coated sheet had been made and dried in accordance with the procedure of Example I, a coating of carbon black was deposited over the zinc oxide coating in subdued light from a suspension of carbon black and binder in a solvent. The suspension contained 1.8 grams of acetylene carbon black, 20 grams of Pliolite (30 weight percent solids in toluene), 46 grams of ethyl acetate and 33 grams of toluene. The suspension was prepared by ball-milling the mixture with steel balls for 12 to 18 hours. The wet thickness of the carbon black layer was about 2 'mils, and after airdrying in the dark at 23 C. the thickness of the carbon black layer was about 0.15 mil.

The completed and dried receptor had approximately the following electrical characteristics: A. Measured with conductive rubber electrode applied electric field: 10 volts per mil (1) Etfective average conductivity:

Dark 1.3 10* mho/cm. Exposed sec., 500 ft. candles, 3150 K.

9.4 mho/cm.

(2) Estimated lateral surface resistance /t without conductive backing Thin carbon black film on paper-dark or exposed ohms/square 4 10 Film 0.75 mil thick on Mylar Resistivity=5 ohm cm.

R =2700 ohms per square Exposed 5 sec., 500 ft. candles, 3150 K.

1.6 '10 mho/cm. at 6 v./mil.

(2) Effective average anodic conductivity:

Dark 1.4 10 mho/cm. at 46 v./mil. Exposed 1.3 10 mho/cm. at 6 v./mil.

Cathodic transverse resistance p/t:

Dark 1.1 10 ohm cm. at 31 v./mil. Exposed 110 ohm cm. at 6 v./n1il.

(4) Anodic transverse resistance p/ t:

Dark 1.2 10 ohm cm. at 46 v./mil. Exposed 120 ohm cm. at 6 v./mil.

The sheet material prepared as described above was placed in a camera having a lens opening of f 4.5. The light on the subject was equivalent to 500 foot candles tungsten lamp. The lens was focused on the subject at a distance of six feet. An exposure time of 20 seconds was used. The exposed sheet was then removed from the camera in the dark and placed in an aqueous electrolytic developing solution. The electrolytic solution had the following composition: 25 grams of AgNO 55 grams of NaCN, 20 grams of Na cO H O and 550 grams of water. A 16-volt direct current potential was applied between the sheet and the electrolytic solution. The sheet was the cathode, and the electrolytic solution was connected to a silver anode. The development was carried out for seconds at an average current density of about 15 milliamperes per square centimeter. A good positive image was produced.

Example 111 The contrast of the reproduction produced in accordance with Example II could be improved by anodic treatment of the receptor prior to use for reproduction purposes. Such anodic treatment of the receptor of Example II was effected by flooding the photo-sensitive surface of the receptor with light and then immersing the sheet or receptor in an aqueous electrolyte solution containing sodium chloride and passing a 20 to 30 milliampere direct current for about 2 minutes through the aqueous solution and receptor While the receptor is connected with the positive pole of the direct current source and the aqueous solution with the negative pole. The reflectance of the silver deposit formed as in Example II, after anodic treatment, was about 90 percent as compared to 70 percent without anodic treatment of the receptor.

10 Example IV This example relates to the use of a conductive zinc oxide layer deposited upon the photoconductive zinc oxide layer. A paper-aluminum laminate was treated to deposit a second aluminum layer upon the aluminum of the laminate. The aluminum was deposited by vapor deposition to a thickness of 0.05 micron. This was done in order to assure direct and electrical contact between the photoconductive layer and the aluminum layer. In some cases, aluminum foil contains a non-uniform insulating layer which is primarily aluminum oxide. The vapor deposition of aluminum on the aluminum foil overcomes this problem.

A mixture of photoconductive zinc oxide having the following composition was prepared:

This mixture was ball-milled 22 hours with /2-inch diameter porcelain balls in a one-gallon jar. Phosphine-R dye was added to give 0.02 weight percent dye solids relative to zinc oxide. The Phosphine-R was dissolved in methanol in an amount equivalent to 0.003 gram of dye per milliliter of methanol and 2.8 cos. of this solution was added to grams of the above Zinc oxide mixture. The dyed photoconductive zinc oxide mixture was knife-coated upon the aluminum layer to a 4-mil thickness and allowed to air-dry at room temperature. The conductivity this zinc oxide layer was about 16* to 10 mho/cm. in the light and less than about 10" mho/ cm. in the dark.

A second zinc oxide mixture was prepared, having the following composition:

Grams High conductivity zinc oxide (non-photoconductive) Pliolite (30% solids in toluene) 133 Toluene 44 Acetone 25 This highly conductive zinc oxide mixture was ball-milled 18 hours with /2-inch diameter porcelain balls. The above high conductiivty zinc oxide mixture was further diluted with acetone and toluene such that the proportion of the above zinc oxide mixture to added acetone to added toluene was 10: 1:5 by weight. The diluted mixture was knife-coated upon the photoconductive layer of the receptor at a 2-mil thickness. The coating was air-dried at room temperature in the dark. The resulting sheet was a pale yellow. The conductive zinc oxide top layer had a conductivity of about 10* mho/cm. in both the dark and in the light.

The above receptor was exposed 5 to 10 seconds to a projected continuous tone light image. The photographic negative image which was projected was enlarged four times. The light intensity at the plane of the photoconductive sheet was 300 foot candles (3150 K). A black and white reproduction of the projected image was de veloped upon the Zinc oxide surface of the receptor by electro-depositing silver upon the light-struck areas from a silver nitrate-thiourea aqueous electrolyte solution. The photoconductive receptor sheet was made the cathode, and a stainless steel electrode inserted in the aqueous electrolyte was made the anode. The applied voltage was 60 volts direct current, and the average current density was 15 milliamperes per cm. The development time was 1 second. The result was a negative reproduction of the projected image.

Because of the highly conductive zinc oxide top or front surface of the receptor, the receptor of the above example can be connected to the cathode directly through the front surface, as well as by direct contact with the aluminum layer. In connecting the cathode to the zinc oxide front surface, electrical current passes directly through the Zinc oxide film to the conducting backing opposite the point of contact. Without the surface coating of conductive Zinc oxide, direct contact with the cathode cannot usually be made through the zinc oxide surface because of contact resistance and rectification of the zinc oxide. As previously stated, photoconductive zinc oxide rectifies at such a contact with an electrolytic solution, but the conductive surface on the zinc oxide layer eliminates this rectification. The cathode contact may conveniently constitute a conductive rubber roller or a sponge containing an aqueous electrolytic solution, allowing direct contact to the front surface of the receptor. Front contact development as above described is performed at the usual current density with about twice the voltage used when he electrical contact is made directly to the conductive aluminum layer of the receptor.

Example V The photoconductive copysheet of Example II was utilized to make a reproduction using a polymer latex solution containing an electrolyte. The photoconductive sheet was first exposed as in Example I to a light image.

The sheet was then suspended in a 1% solids aqueous polyethylene latex [A-C Polyethylene 629, Allied Chemical and Dye Company, M.P. 213-221 F., penetration (100 grams, seconds, 77 F.) of 3 to 6, acid No. l4 17, color less than 1 NPA]. Using the conductive aluminum sheet as the positive pole, the polyethylene latex was electrolyzed at a potential of about 30 to 40 volts for about 15 seconds. Polyethylene was deposited selectively on those light-struck areas producing a white polyethylene image which had greater ink receptivity relative to the zinc oxide background areas. When used as a lithographic plate, negative prints were obtained. If the original light image is negative, the final lithographic prints are positive.

Other polymeric latices which are stable in alkaline media and which contain negatively charged particles can be similarly employed, including polytetrafluoroethylene, synthetic rubber, e.g. Chemigum latex 245-B (butadieneacrylonitrile, non-staining, oil-resistant, vulcanizable synthetic rubber latex supplied by the Goodyear Tire and Rubber Company), polyvinyl acetate, polystyrene, Pliolite, rubber, polyvinylidene chloride (Saran), Versamid 100 (polymer of a fatty acid and a polyamine, amine value 83-93), etc.

Inclusion of titanium dioxide suspension in the latex improves the whiteness of the deposited polymer.

Example VI A conductive Zinc oxide coated photoconductive sheet was prepared and exposed as described in Example IV. Using the conductive aluminum layer as the positive pole, a sponge containing a dilute aqueous solution of p-amino diethyl-aniline, p-nitro-benzyl cyanide and sodium sulfite was connected to the negative pole of the current source and was slowly drawn over the differentially conductive surface. A potential of 30 to 40 volts was used. A magenta colored image was thereby electrolytically developed, the p-aminodiethyl-aniline developer being oxidized, and coupling with the p-nitro-benzyl cyanide to produce the magenta color on these light-exposed surface areas.

When alpha naphthol and ethyl aceto-acetate were substituted as couplers, the resulting images were cyan and yellow, respectively. Other oxidizable developers, such as phenolic compounds, eg pyrogallic acid, etc., can be used in place of p-arninodiethyl-aniline.

Example VII The black photoconductive paper of Example II was used to make a positive image, yellow on black. The black photoconductive paper was exposed to a light image in a similar manner as in the preceding examples. The latent image thus produced was developed cathodically with an aqueous electrolyte solution containing 5 weight percent magnesium chloride. The light-struck areas as I2 sumed a basic pH during electrolysis. Thereafter, an aqueous solution of methyl orange was applied to this surface resulting in a visible yellow image on black.

Example VIII This example illustrates the use of a black silver deposit in silica upon the photoconductive Zinc oxide layer of a receptor. The receptor prepared in accordance with Example I was top-coated with colloidal silica by dip-coating in an aqueous suspension containing finely divided colloidal silica in an amount by weight equivalent to water. The receptor was then dried and tests indicated that about 3 grams of colloidal silica per square meter was deposited on the surface of the receptor. The thickness of the silica layer was about 1 micron. The entire sheet or receptor containing the coating of silica was then light-exposed and black silver was deposited on the exposed sheet by electrolysis using an aqueous electrolyte solution containing silver nitrate and thiourea. The cathode -was connected directly to the aluminized backing and the positive electrode was contacted with the aqueous electrolytic solution. The voltage was about 30 volts per mil thickness of the Zinc oxide film and about 40 milliamperes per square centimeter of direct current was utilized. The time required to deposit a uniform black layer of silver over the entire area con tacted by the electrolyte of the receptor was 2 to 4 seconds. The resulting sheet had a glossy black surface with a reflection optical density between about 1.4 and about 2.0. The silver deposited as described increases the conductivity of the top surface whereby good electrical conduction from the front of the receptor to the zinc oxide film was achieved under dry conditions.

The above sheet was exposed to a light image and the latent light image was electrolytically developed with sodium silver cyanide as in Example II. The silver deposited in the light-struck areas had high reflectance and appeared white.

Similarly, the sheet was exposed and electrolytically developed in accordance with Example V using an aqueous electrolyte containing a water-soluble Versamid l00-HCl, and containing suspended titanium dioxide. Upon electrolysis, the Versamid deposited upon the light-struck areas and the suspended titanium dioxide adhered to the deposited Versamid 100. The alkaline conditions during electrolysis at the light-struck areas caused the water-soluble Versamid 100 to precipitate. The result was a white deposit of titanium dioxide on the light-struck areas, giving a good reproduction. The aqueous solution containing the Versamid 100 and titanium dioxide had approximately the following composition with regard to these components:

Grams Colloidal titanium dioxide 20 2 weight percent Versamid 100 solution 200 Water 200 The mixture was then ball-milled at least 24 hours with /z-inch diameter glass balls.

The solution of the Versamid 100 was prepared by dissolving 77 grams of Versamid 100 in 308 milliliters of ethyl alcohol. Then, to this solution was added 5.05 milliliters of 'HCl in 280 milliliters of water. This mixture then was diluted with water to 3780 milliliters.

Example IX The construction of the receptor of Example II can be utilized to make a transparency by using a transparent conductive receptor or plate such as those known in the art. For example, vapor coating of gold on mylar or conductive tin oxide on glass are suitable transparent conductive films or plates. The transparent conductive receptor was made the cathode, and the receptor of Example II was made the anode. An electrolyte solution containing silver nitrate and thiourea was placed between the receptor of Example II and the transparent conductive receptor. An image was projected through the transparent conductive receptor and electrolysis was eifected during image projection. Silver -was electro-deposited upon the transparent conductive receptor opposite the light-exposed areas of the photoconductive receptor of Example 11 to form a negative transparent image copy. If the transparent conductive image receptor is coated with a thin film of carbon black in a binder, a positive image can be developed with an aqueous electrolyte containing sodium silver cyanide.

Example X The construction of Example II can be utilized to make a permanent latent image which can be developed as much as a month later. In this example the receptor was prepared and exposed to a light image or pattern in accordance with Example II, then the exposed sheet was developed with an aqueous solution containing sodium chloride as the electrolyte and developer. No silver salt or other materials were used. The aluminum layer of the receptor was connected to the cathode, but connection to the anode works equally well. Latent image was developed in about 15 seconds using 16 volts and a current density of about 15 milliamperes. The receptor was set aside for about a month; then the latent image on the receptor was developed electrolytically in accordance with the development procedure of Example II. A good positive black and white image was produced with good contrast and detail.

The first development step to produce the permanent latent image was also carried out with a silver thiosulfate aqueous solution, but in this case the aluminum layer of the receptor must be connected to the anode to prevent deposition of silver on the receptor.

Various other modifications and alterations of the paper and processes may become apparent to those skilled in the art without departing from the scope of this invention.

Having described my invention, I claim:

1. An integral reproduction receptor consisting essentially of an opaque substrate comprising a laterally-conductive metal layer, an intermediate layer comp-rising a photoconductor conductively bonded to said metal layer, and a subsequent radiation penetrable solid layer having more conductivity in at least one polarity direction than said intermediate layer and substantially coextensive with and conductively bonded to said intermediate layer comprising granular conductive material uniformly disposed laterally throughout said subsequent layer.

2. A reproduction receptor consisting essentially of an opaque substrate comprising an insulating support having aifixed to the surface thereof a continuous laterallyconductive metal layer, an intermediate photoconductive layer comprising a particulate photoconductor and an insulating resinous binder conductively bonded to said metal layer, and a subsequent radiation penetrable solid substantially non-photoconductive layer comprising a granular conductive material uniformly disposed laterally throughout said subsequent layer and having more con ductivity in at least one polarity direction than said intermediate photoconductive layer substantially coextensively overlying and conductively bonded to said intermediate layer.

3. An integral reproduction receptor consisting essentially of an opaque substrate comprising a laterally-conductive aluminum layer, an intermediate layer comprising photoconductive zinc oxide conductively bonded to said metal layer, and a subsequent radiation penetrable solid substantially non-photoconductive layer having more conductivity in at least one polarity direction than said intermediate layer and substantially coextensive with and conductively bonded to said intermediate layer comprising granular conductive material uniformly disposed 1d laterally throughout said subsequent layer in a thickness not greater than about 10 microns.

4. The receptor of claim 2 in which said subsequent layer comprises carbon black.

5. The receptor of claim 2 in which said subsequent layer comprises conductive zinc oxide.

6. The receptor of claim 2 in which said subseuent layer comprises conductive titanium oxide.

7. The receptor of claim 2 in which said subsequent layer comprises conductive titannous oxide.

8. The receptor of claim 2 in which said subsequent layer comprises conductive lead sulfide.

9. A process for making a reproduction which comprises exposing to a lgiht image a reproduction receptor consisting essentially of an opaque substrate containing a continuous laterally-conductive metal layer thereon, an intermediate photoconductive layer conductively bonded to said metal layer, and a subsequent radiation penetrable solid conductive layer substantially coextensively overlying and conductively bonded to said photoconductive layer having more conductivity in at least one polarity direction than said photoconductive layer comprising granular counductive material uniformly disposed laterally throughout said subsequent layer to create a latent image on said receptor, wetting the surface of the receptor with an aqueous electrolyte solution containing a developer material, creating an electrical potential be tween the metal layer of said receptor and said aqueous electrolyte solution to produce a current and thereby visibly developing said latent image as a reproduction on said receptor.

10. The process of claim 9 in which said metal layer is the cathode.

11. The process of claim 9 in which said metal layer is the anode.

12. The process of claim 9 in which said receptor prior to exposure has been anodically treated in an aqueous electrolyte.

13. A process for making a reproduction which comprises exposing to a light image a reproduction receptor consisting essentially of an opaque substrate containing a continuous laterally-conductive aluminum layer thereon, an intermediate photoconductive zinc oxide layer conductively bonded to said metal layer, and a subsequent radiation penetrable solid substantially non-photoconductive layer substantially coextensively overlying and conductively bonded to said photoconductive layer having more conductivity in at least one polarity direction than said photoconductive layer comprising granular conductive material uniformly disposed laterally throughout said subsequent layer in a thickness not greater than about 10 microns to create a latent image on said receptor, wetting the surface of the receptor with an aqueous electrolyte solution containing a metal salt developer material,

creating direct current electrical potential between the metal layer of said receptor and said aqueous electrolyte solution to produce a current and thereby visibly developing said latent image as a reproduction on said receptor.

14. A process for making a positive reproduction which comprises exposing to a light image a reproduction receptor consisting essentially of an opaque substrate containing a continuous laterally-conductive metal layer thereon, an intermediate photoconductive layer substantially coextensive with and conductively bonded to said metal layer and a subsequent radiation penetrable solid conductive layer comprising carbon black uniformly disposed laterally throughout said subsequent layer and conductively bonded to said photoconductive layer havmg more conductivity in at least one polarity direction than said photoconductive layer, to create a latent image on said receptor, wetting the surface of the receptor with an aqueous electrolyte solution containing a silver salt developer material, creating direct current electrical potential between the metal layer of said receptor as the cathode and said aqueous electrolyte solution as the anode to pro- References Cited in the file of this patent UNITED STATES PATENTS Miller Oct. 31, 1939 Dalton Dec. 29, 1953 Berchtold Dec. 30, 1958 MoncrietT-Yeates Sept. 15, 1959 Johnson et a1 Nov. 28, 1961 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3 127,333 March 31 1964 Leon O Bonrud It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 10, line 31, after "conductivity" insert of line 32, for "16 read 10- Signed and sealed this 4th day of August 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

9. A PROCESS FOR MAKING A REPRODUCTION WHICH COMPRISES EXPOSING TO A LIGHT IMAGE A REPRODUCTION RECEPTOR CONSISTING ESSENTIALLY OF AN OPAQUE SUBSTRATE CONTAINING A CONTINUOUS LATERALLY-CONDUCTIVE METAL LAYER THEREON, AN INTERMEDIATE PHOTOCONDUCTIVE LAYER CONDUCTIVELY BONDED TO SAID METAL LAYER, AND A SUBSEQUENT RADIATION PENETRABLE SOLID CONDUCTIVE LAYER SUBSTANTIALLY COEXTENSIVELY OVERLYING AND CONDUCTIVELY BONDED TO SAID PHOTOCONDUCTIVE LAYER HAVING MORE CONDUCTIVITY IN AT LEAST ONE POLARITY DIRECTION THAN SAID PHOTOCONDUCTIVE LAYER COMPRISISNG GRANULAR CONDUCTIVE MATERIAL UNIFORMLY DISPOSED LATERALLY THROUGHOUT SAID SUBSEQUENT LAYER TO CREATE A LATENT IMAGE ON SAID RECEPTOR, WETTING THE SURFACE OF THE RECEPTOR WITH AN AQUEOUS ELECTROLYTE SOLUTION CONTAINING A DEVELOPER MATERIAL, CREATING AN ELECTRICAL POTENTIAL BETWEEN THE METAL LAYER OF SAID RECEPTOR AND SAID AQUEOUS ELECTROLYTE SOLUTION TO PRODUCE A CURRENT AND THEREBY VISIBLY DEVELOPING SAID LATENT IMAGE AS A REPRODUCTION ON SAID RECEPTOR. 